1. Field of the Invention
The present invention relates to video trackers for electro-optical systems, and, more particularly, to video trackers which are responsive to a linear video signal to provide azimuth and elevation error signals that are normalized with respect to the displacement of the volumetric centroid of the target from the center of the tracking window.
2. Description of the Prior Art
In the prior art, video trackers have been developed for controlling the scanning of a sensor in an electro-optical tracking system. Generally, these prior art trackers employed a threshold mechanism to produce binary video signals, sometimes also referred to as black/white video signals. These binary video signals are then processed to provide azimuth and elevation error signals for controlling the scanning of the sensor. However, these threshold type trackers required a means to determine the appropriate threshold value at which the threshold mechanism was to operate and a means to maintain the established threshold value. These means for determining and maintaining the appropriate threshold value required relatively complex and, consequently, expensive circuitry making these threshold type trackers too expensive for use in an austere electro-optical tracking system in which the tracking function must be performed with minimum cost and circuit complexity.
Another type of video tracker used in prior art electro-optical systems differentiated the video signals to detect target edges. However, this type of tracker has proven to be susceptible to false targets produced by background clutter returns. Also, as with the threshold type trackers, these differentiation type trackers required circuitry of a complexity that made them too expensive for use in austere electro-optical tracking systems.
Also, prior art trackers have developed mechanisms for regulating the azimuth and elevation error signals in terms of volts per degree of measured error or other suitable measurement parameter. However, these error signal regulated trackers had significant limitations, such as, for example, the requirement that the target be completely enclosed within the tracking window.
Therefore, there was a need in the prior art for a tracker of relatively low circuit complexity making it suitable for use on austere electro-optical tracking systems, but which would, nevertheless, provide adequate tracking performance. Also, there was a need in the prior art to regulate, or normalize, the tracking error signals with respect to a suitable measurement parameter such that the normalization process would be operative over a broad range of potential tracking conditions.